Intracellular filamentous inclusions containing abnormally phosphorylated tau protein are hallmarks of several human neurodegenerative disorders. This study reveals tau-positive cytoskeletal abnormalities in neurons and glial cells of aged baboons. The brains of four baboons (Papio hamadryas, 20-30 yr of age) were examined using the Gallyas silver technique for neurofibrillary changes and phosphorylation-dependent anti-tau antibodies (AT8, AT100, AT270, PHF-1, TG-3). Conspicuous changes were noted in two animals, 26 and 30 yr of age. In both animals, a combination of neuronal and glial cytoskeletal pathology was seen preferentially affecting limbic brain areas, including the hippocampal formation. In the 30-yr-old animal, numerous tau-positive inclusions were seen in the granule cells of the fascia dentata. These cells even exhibited an accumulation of argyrophilic neurofibrillary tangles. The glial changes affected both astrocytes and oligodendrocytes. Tau-positive astrocytes were seen in perivascular, subpial, and subependymal locations. Tau-positive oligodendrocytes preferentially occurred in limbic fiber tracts including the entorhinal perforant path. Ultrastructurally, tau-positive straight filaments (10-14 nm) in both neurons and glial cells were revealed by anti-tau immunoelectron microscopy. This study thus indicates the potential usefulness of aged baboons for experimental investigation of neuronal and glial filamentous tau pathology. This nonhuman primate species may provide valuable information pertinent to the broad spectrum of human tauopathies.

The glial-limiting membrane at the border of the central nervous system (CNS) consists of glial endfeet covered by a basal lamina. The formation of the glia limitans seems to be controlled by adjacent meninges but only little is known about this interaction. In the present study astrocytes and meningeal cells were investigated in vitro to see if cocultures of these cells can serve as a suitable model for the differentiation of the glial-limiting membrane and can be used to define the conditions under which the glial-limiting membrane develops. The following observations were made in cocultures of meningeal and astrocytic cells of two-day-old rats: (i) epithelioid astrocytes were transformed into stellate cells; (ii) single colonies of proliferating epithelioid astrocytes were generated; (iii) the area around these colonies becomes devoid of meningeal cells, which seem to form a circular border around the astroglial islands; (iv) from the glial colonies long thin glial processes grow towards the surrounding meningeal cells, terminating at the site of contact; (v) in the contact zone between meningeal cells and astrocytes irregular shaped deposits of electron dense material resembling a basal lamina were seen. These observations indicate that indeed a structure resembling a glial-limiting membrane develops in cocultures of meningeal and astrocytic cells. Its formation depends on the balance of growth promoting effects of meningeal cells on astrocytes and growth inhibiting effects of astrocytes on meningeal cells. Both activities can be enriched from conditioned media of pure astrocytic or meningeal cell culture. The proposed model of meningo-astrocytic cocultures may be a helpful instrument for further investigations on the formation of the glia limitans.

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The carbohydrate epitope 3-fucosyl-N-acetyllactosamine (CD 15) is involved in cell-to-cell recognition processes in various tissues. In the CNS of the adult rat, immunoreactivity for CD 15 reveals a region-specific distribution pattern by light microscopy. In the present study we investigated the ultrastructural localization of CD 15 in the rat brain using preembedding immunocytochemical methods. In addition we studied CD 15 expression in cultured astrocytes from optic nerves of 11-day-old rats. In optic nerve sections, immunostaining was found on the surface of astrocytes at various contact sites, i.e. astrocyte-astrocyte, astrocyte-oligodendrocyte, astrocyteaxon myelin, and astrocyte-blood vessel contacts. Oligodendrocyte-oligodendrocyte contacts, however, were always negative. In the telencephalic cortex, CD 15 immunoreactivity was found in glial cell processes around synapses and in the cerebellar cortex in Bergmann glial cells. In astrocytes grown in serum-containing medium, CD 15 was expressed on the surface of fibroblast-like glial fibrillary acidic protein-positive astrocytes, which were identified as type 1 astrocytes as well as on process-bearing A2B5-positive cells, representing type 2 astrocytes. The present data support the assumption that in the adult rodent brain, CD 15 is exclusively expressed by astrocytes. The in vivo distribution of this carbohydrate molecule on distinct astroglial contact sites supports the notion that CD 15 could act in cell-to-cell recognition processes.

The adult mammalian central nervous system (CNS) reacts to a penetrating injury with the formation of a glial scar consisting of a newly formed glia limitans accessoria, basement membrane and meningeal fibroblasts. By contrast, in fetal and perinatal mammals a similar injury evokes only a reduced reactive astrogliosis, and a typical astroglial scar begins to develop only when the lesion has been placed beyond a critical developmental period. In the present investigation we have tested the hypothesis that IL-1 beta plays a pivotal role in the process of cicatrization, by investigating whether immature animals develop a glial scar after IL-1 beta is injected into their CNS. Adult female rats were given injections of 2U recombinant IL-1 beta or PBS alone in the contralateral cortex in identical positions of the cerebral hemispheres. Postnatal day 2 (P2) rats received injections of either 1U IL-beta or PBS into the lateral aspect of the frontal cortex on each side. The animals were sacrificed 4 and 14 days post injection and the perilesional area was assessed for astrogliosis (expression of GFAP-immunoreactivity and the activity of glutamine synthetase), neovascularization (laminin-immunoreactivity on blood vessels at the lesion site), and the formation of a gliomeningeal scar (GFAP- and laminin-immunoreactivity at the lesion site). Using similar criteria for the evaluation, we found that in adult animals some of the processes associated with cicatrization are augmented. In the immature animals, however, the formation of the glio-meningeal scar is not altered by IL-1 beta, i.e. it remains absent. We conclude that IL-1 beta augments some responses of the cells involved in wound healing in the adult CNS, but does not alter key mechanisms operative in the reaction of the brain to a penetrating injury, as shown by its inability to alter the stage specific response of the immature brain.

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There is considerable debate on the development of a glial cell line in the rat optic nerve, which is characterized by the specific expression of the A2B5 and HNK-1 epitopes. This cell line has been assumed to give rise to oligodendrocytes and so-called type 2 astrocytes. However, it is doubtful that the latter cell type really exists in vivo. In the present study, we have addressed this question by investigating the development of astrocytes in the myelin-deficient (md) rat, which is characterized by dysmyelination and loss of oligodendrocytes. Defective oligodendrocytes were observed by the third postnatal day, well before the generation of type 2 astrocytes. Consequently, the number of type 2 astrocytes was reduced in cultures prepared from optic nerves of md rats vs. controls. This finding was not paralleled in vivo; i.e., no dying astrocytes were observed in md sections by conventional electron microscopy. However, immunoreactivity against the HNK-1 epitope was enhanced in md compared to control sections. Ultrastructurally, HNK-1 immunoreactivity was detected predominantly on the axonal surface at astroaxonal contact sites, which were found only at the nodes of Ranvier within controls but extended to the whole axonal surface in md animals. Only a minor portion of the immunoreactivity derived from glial cells, presumably from oligodendrocytes at the paranodal region in controls. Thus, the HNK-1 epitope is not a useful antigen for distinguishing astrocytes in the rat optic nerve. Accordingly, our results do not provide evidence for the existence of specialized type 2 astrocytes in vivo. In vitro, these cells are probably only oligodendrocytes that mimic some astroglial features if grown in serum-containing media.

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